1. Prior Art
Recent improvements in the spatial and data resolution capabilities of digital color image processing systems have made such systems particularly attractive for a variety of photo-processing (e.g. photo-finishing) applications. In still color image photography, for example, once an image (such as that captured on color photographic film or a high resolution color digital camera) has been digitized and stored in an attendant data base, it is readily optimized for reproduction by means of photofinishing image processing software. One example of a color photo-finishing system that takes advantage of this capability is disclosed in co-pending patent application Ser. No. 582,305, filed Sep. 14, 1990, by S. Kristy entitled "Multiresolution Digital Imagery Photofinishing System," assigned to the assignee of the present application and the disclosure of which is herein incorporated.
As described in that application, conventional photo-finishing of consumer-generated still color photographs (e.g. those captured on 35 mm color film) involves the use of an analog electro-optic system and an associated chemical-based print developing unit. In the above-referenced Kristy application, there is described a digital image-based photofinishing apparatus that enables the personal customizing and obtaining of high quality prints of photographic images; it also provides for the storage and retrieval of high resolution digitized color still images for playback to a variety of reproduction devices.
To this end, as diagrammatically illustrated in FIG. 1, the digital-image-based photofinishing apparatus employs a high resolution opto-electronic film scanner 12, the output of which is coupled to a digitized image processing computer 14. Scanner 12 may comprise a commercially available Eikonix Model 1435 high resolution scanner, having a very high resolution sensor pixel array (a 3072.times.2048 pixel matrix) capable of generating high spatial density-representative output signals which, when converted into digital format, yield `digitized` photographic image files from which high quality color prints may be obtained. Scanner 12 is arranged to be optically coupled with a photographic recording medium, such as a conventional 35 mm color film strip 16. Film strip 16 typically contains a plurality (e.g. a set of twenty-four or thirty-six) 36 mm .times. 24 mm color image frames. For each scanned image frame, scanner 12 outputs digitally encoded data, representative of the opto-electronic response of its high resolution imaging sensor pixel array, onto which a respective photographic image frame of film strip 16 is projected by the scanher's input lens system.
This digitally encoded data, or `digitized` image, is supplied to computer 14 as digitized image pixel signals R,G,B forming an imaging pixel array-representative bit map, resolved to a prescribed code width (e.g. eight bits per color per pixel). Computer 14 contains an image encoding and storage operator through which each high resolution digitized image file is stored in memory. In one mode of operation pertinent to the present invention, the image digital data is processed in computer 14 by reference to code data stored in a lookup table 14a to derive a second set of digital data R',G',B' which is the complement of the input image data. This complement image is the negative image to be printed by a digital color printer 22 onto a non-photographic recording medium 24 and, ultimately, to be used in producing a final positive print image. Optionally, the digital image data may be exchanged with a separate image processing workstation 20 programmed to allow for interactive operations allowing an operator to modify the image data in any desired manner to achieve a pleasing image in the final print. Although the computer 14 is shown as a unit separate from the workstation 20, the functions of the two may, in fact, be incorporated into a single unit.
A high spatial resolution digital output device, such as a digital thermal color printer, is able to provide a high quality hard copy of a customized image directly from the digital data base; in which case the R',G',B' signals would represent a positive image rather than the compliment or negative of the image. However, printing with a high resolution printer of this type is a relatively slow process. Also, because the output reproduction medium (e.g. thermal color print paper) upon which the image is written, is not inexpensive, the price per print remains substantially high, regardless of the number of copies made.
In a conventional analog optical/chemical photofinishing process, on the other hand, multiple copies of an original image can be made through repeated illumination of a negative onto sheets of relatively inexpensive photo-sensitive color print paper, such as Ektacolor (Trademark Eastman Kodak Co.) color print paper and chemically developing the exposed sheets during a reasonably abbreviated processing sequence. Unfortunately, purely optical/chemical processing systems do not offer the flexibility and processing capability of digital image processing systems.
For many years, negative films have employed colored couplers which give the film an orange appearance, referred to as an "orange mask", particularly in the unexposed exposure areas of the film (corresponding to white or near-white areas in the final print). While it is not absolutely necessary to incorporate the orange mask into a negative to be printed, there is a definite advantage. The orange mask partially compensates for the unwanted spectral absorptions in the three dye layers (cyan, magenta, yellow) of the negative film and in the overlapping spectral sensitivities of the photographic paper and gives a dramatic improvement in the color reproduction of the film/paper system.
There are several ways of printing onto photographic paper if no orange mask is incorporated into the negative. In order to get acceptable color balance in neutral areas of prints when printing a negative that has no orange mask, the filtration of the light source used to expose the negative to the photographic print material must be changed by an amount equivalent to the average density of the orange mask. This can be done in one of several ways. The cyan, magenta, and yellow filters in the optical path of the light source can be adjusted to compensate for the absence of the orange mask. Unfortunately, some printers do not have a sufficiently large adjustment range to accommodate such a change. Alternative approaches are disclosed in commonly assigned U.S. Patent Application Ser. No. 631,708 - Manico et al, filed Dec. 12, 1990. In one such alternative, a sheet of translucent "orange" filter material of the proper density is laid over the negative to form a lamination used to expose the print material. While useful for the purpose, this technique has a disadvantage in that the orange filter must be very uniform and have no "blemishes" since it is in the focal plane of the negative. In another such alternative, which is particularly applicable to a system in which the image has been digitized and stored as a digital data base, the digital image is printed onto an intermediate non-photographic recording material to form the internegative and the orange mask is digitally incorporated into the digital image data. This is done by graphically modeling the masking that exists in conventional negative film and modifying the printer look-up tables used for printing the digital image to incorporate data values that result in emulation of the orange mask. The dyes printed by the thermal printer onto the intermediate material incorporate the adjusted color balance needed to emulate the orange mask and the resulting prints photochemically produced on conventional photographic print materials then have substantially similar color characteristics to those made from conventional negatives.